1. Field of the Invention
The present invention relates to disk drives for computer systems. More particularly, the present invention relates to a disk drive employing a calibrated brake pulse to reduce acoustic noise when latching an actuator arm.
2. Description of the Prior Art
FIG. 1A shows a prior art disk drive 2 comprising a disk 4 and a head 6 actuated over the disk 4 by a voice coil motor (VCM). The head 6 is connected to the distal end of an actuator arm 8 which is rotated about a pivot 10 in order to actuate the head 6 radially over the disk 4. The VCM comprises a voice coil attached to the actuator arm 8 having a first leg 12A and a second leg 12B for conducting current in a clockwise or counterclockwise direction thereby generating a magnetic flux which interacts with the magnetic field of permanent magnets (not shown) to generate a torque to rotate the actuator arm 8 about the pivot 10 in a clockwise or counterclockwise direction. The disk 4 comprises a plurality of tracks 14 defined by a plurality of embedded servo sectors 16, wherein disk drive control circuitry processes the embedded servo sectors 16 in order to seek the head 6 to a target track and maintain the head 6 over the target track during read/write operations.
When the disk drive is powered down (or otherwise idle), the disk drive control circuitry will perform a park operation wherein the head 6 is parked and the actuator arm 8 is latched. In the embodiment of FIG. 1A, the head 6 is parked on a landing zone 18 by rotating the actuator arm 8 in the counterclockwise direction. While the head 6 is parked, the actuator arm 8 is “latched” to prevent it from rotating the head 6 away from the landing zone 18. In the embodiment of FIG. 1A, a magnet 20 attached to a crash stop 22 attracts and holds a metal tang 24 attached to the actuator arm 8.
A problem with using a magnet as a passive latching mechanism is the undesirable acoustic noise generated when the tang 24 collides with the magnet 20 (or the crash stop 22 if the magnet 20 is embedded into the crash stop 22). A prior art technique for latching the actuator arm 8 applies a constant latching current to the voice coil to accelerate the actuator arm 8 until it latches. As the tang 24 approaches the magnet 20, the exponential increase in the force of the magnet and the corresponding increase in the acceleration of the actuator arm 8 further exacerbate the acoustic noise when the tang 24 collides with the magnet 20.
U.S. Pat. No. 6,441,987 discloses a technique for latching the actuator arm 8 by applying an alternating latching current (e.g., a square wave) to the voice coil instead of a constant latching current which reduces the acceleration of the actuator arm 8 as the tang 24 moves toward the magnet 20. However, the characteristics of the alternating latching current remain constant (e.g., constant duty cycle) throughout the latching operation which means a certain amount of undesirable acoustic noise will still occur when the tang 24 collides with the magnet 20.
There is, therefore, a need to reduce acoustic noise in a disk drive when latching the actuator arm.